The present invention relates to integrated circuits. In particular, the present invention relates to analog temperature measurement in integrated circuits.
Heat produced by electric current in integrated circuits becomes more problematic as the operating frequencies and transistor densities of integrated circuits continue to increase. A densely integrated, high frequency circuit, such as a microprocessor, may be able to generate enough heat to permanently damage itself. Many such integrated circuits include internal temperature sensors so that, when internal temperatures approach critical levels, the circuits can be shut down or their operating frequencies can be reduced so as to generate less heat.
Measuring external temperature an also be important. For instance, if the temperature around an integrated circuit is above a certain level, the integrated circuit may not be able to dissipate enough heat to sustain prolonged high frequency operation. In which case, depending on the external temperature, an operating frequency for an integrated circuit may be adjusted to sustainable levels.
A diode is commonly used as a temperature sensor in and around integrated circuits. For a given current, voltage across a diode is dependent on temperature. By measuring the voltage across a diode for two different known currents, the temperature of the diode can be calculated. That is, temperature is proportional to the voltage difference across a diode for two known currents. The relationship can be expressed as:       T    =                            K          ⁢                      (                                          V                1                            -                              V                2                                      )                          /        Ln            ⁢              xe2x80x83            ⁢              (                              I            1                                I            2                          )              ,
where T is temperature in Kelvin,
K is a constant,
I1 and I2 are known currents, and
V1 and V2 are voltages measured across the diode at currents I1 and I2 respectively.
Temperature can be measured wherever a temperature sensor can be located. For instance, a microprocessor may include an internal diode for sensing the junction temperature inside the microprocessor. A chassis for housing a microprocessor may include one or more diodes for sensing the environmental temperature around the microprocessor.
Remote circuitry is usually used to measure the temperature in or around an integrated circuit element. For instance, circuitry to measure the temperature inside a microprocessor is often located on the motherboard to which the microprocessor is coupled. Remotely locating the measurement circuitry has numerous advantages such as less susceptibility to damage from the heat source, independent access to a power supply so that if a heat producing component is shut down to prevent over heating the measurement circuitry can continue to measure the temperature and indicate when the component can safely be brought back on line, etc.
In many devices, especially portable devices, very little space is left unused on a motherboard. A typical motherboard may need room for a large number of components, including processor packages, memory cards, input/output ports, etc., as well as a large number of traces and buses to connect all the components. A great deal of effort has been devoted to reducing the complexity and cost of motherboard designs. As market pressures continue to push toward more compact devices with greater functionality, the need for available space on motherboard designs will continue to grow.
A temperature measurement device includes at least one constant current generator to provide a first current and a second current to a temperature sensor, and a signal processing element to provide an analog output signal corresponding to a temperature of the temperature sensor based on a difference between a first voltage of the temperature sensor at the first current and a second voltage of the temperature sensor at the second current.